Dissociation of CuH+ and ZnH+ complexes of ethylenediamine and their N-methylated homologues: Family and neighbours, but not the same

Abstract Upon collisional activation, complexes of CuH + and ZnH + with H 2 NCH 2 CH 2 NH 2 eliminate Cu(0) and Zn(0) to produce protonated ethylenediamine H 2 NCH 2 CH 2 NH 3 + via a proton transfer. Variable collision energy experiments and model chemistry calculations (CBS-QB3 method) indicate that (i) the energy requirement for this process is significantly larger for the zinc complex than for the copper complex; and (ii) the transition-state for the proton transfer is rate-determining for dissociation of the zinc complex, whereas the same process in the copper complex is essentially barrierless. The large activation energy for the zinc complex opens up a competing fragmentation process, viz . loss of NH 3 , which does not occur in the copper complex. N-methyl substitution has no effect for the CuH + complex ions: Cu(0) is lost from the complex (CH 3 ) 2 NCH 2 CH 2 N(CH 3 ) 2 ⋯CuH + . However, a different situation obtains for the complex with ZnH + , which predominantly loses ZnH 2 . Experiment and theory indicate that loss of ZnH 2 is more energy demanding than loss of Zn(0), but that ZnH 2 loss prevails at elevated collision energies.